Lamps used in display lighting commonly include a bulb contained within a generally frustoconical glass envelope. The interior of the envelope is metallized to define a reflector. To provide a whiter light throughout its life, the bulb is filled with gases including halogen gas. When such a lamp burns out, it is simply discarded and replaced with a new one. When used in retail stores and other commercial installations, these lamps are on many hours of each day. Thus, they must be replaced frequently. The combination of the cost of the bulb-within-an-outer-envelope construction and the frequency of replacing the lamp used in display lighting makes such lamps expensive to use.
Outdoor lamps are not as expensive because they do not have an inner bulb and they are not on as many hours in a day. Nevertheless, whenever they burn out, outdoor lamps must be discarded in their entirety. Most vehicle headlamps must also be discarded when the bulb therein burns out.